An inkjet recording apparatus employing a replaceable ink cartridge/ink cartridge bag can be classified into two types. The first type has an ink cartridge and a head provided as a single integral unit. The second type has an ink cartridge and a head provided separately, and also has an ink tank (also referred to as a head tank or a sub tank) connected to the head.
FIG. 1 is a conceptual diagram of an inkjet recording apparatus 10 with the ink cartridges and the head provided as a single integral unit. A recording element substrate is provided on the bottom surface of a box-shaped recording head 11. On top of the recording head 11, there are mounted ink tanks 12k, 12c, 12m, and 12y containing ink of various colors, e.g., black (hereinafter, “k”), cyan (hereinafter, “c”), magenta (hereinafter, “m”), and yellow (hereinafter, “y”). The inkjet recording apparatus 10 further includes a scanner 13, a conveying device 14, a sheet feeding tray 15, and a guide bar 16 of the recording head 11.
In such an inkjet recording apparatus in which the ink cartridge and the head are provided as a single integral unit, the ink flows as follows. Specifically, black ink inside the ink tank 12k is supplied into the recording head 11 through an ink supplying opening of the ink tank 12k and a joint, and is supplied to an ink supplying opening of the not shown recording element substrate through an ink flow path in the recording head 11.
FIG. 2 is a conceptual diagram of an inkjet recording apparatus 20 with ink cartridges and a head provided separately. Ink cartridges 21k, 21c, 21m, and 21y containing ink of various colors as in the example shown in FIG. 1, e.g., black (k), cyan (c), magenta (m), and yellow (y) are provided at the bottom part of the main unit of the inkjet recording apparatus 20. Ink tanks (sub tanks) 22k, 22c, 22m, and 22y for storing ink are mounted on top of the recording head 11. Although not shown, there are ink supplying needles with sharp tips provided in the main unit of the inkjet recording apparatus 20 where the ink cartridges 21k, 21c, 21m, and 21y are set. The ink cartridges are stabbed by these ink supplying needles and connected to the inkjet recording apparatus 20. The other ends of the ink supplying needles are connected to a bendable ink supplying tube 17, so that ink is supplied to an ink tank 22 through the ink supplying tube 17. In FIG. 2, elements corresponding to those in FIG. 1 are denoted by the same reference numbers.
If an inkjet recording apparatus performs a printing operation when there is no ink remaining in an ink cartridge, a desirable printing quality cannot be attained and a failure occurs in the recording head, particularly if the recording head is a thermal type. Furthermore, if an attempt to supply ink is made when there is no ink remaining in an ink cartridge, the pressure decreases in the middle of an ink supplying path or inside the cartridge. This causes air to enter the ink supplying system when the cartridge is replaced subsequently.
In order to avoid the above-described failures, the inkjet recording apparatus needs to have a mechanism for detecting that there is no ink remaining in an ink cartridge (also referred to as an ink end status).
There have been many proposed techniques for determining the remaining amount of ink inside an ink cartridge. As one example of determining the amount of remaining ink, patent document 1 discloses a method of detecting the amount of remaining ink inside an ink cartridge by using an electrode pin. Patent document 2 discloses a method of optically detecting the amount of remaining ink. In both methods, the ink cartridge is provided with additional equipment for detecting the amount of ink remaining inside the ink cartridge, and therefore, the ink cartridge becomes complex and expensive.
Another method of determining the remaining amount of ink is to calculate the amount of ejected ink. However, the ejection amount varies, and therefore, the actual amount of ink consumed may not correspond to the assumed amount of ink consumed. Furthermore, in order to prevent air from entering the ink supplying system, it is necessary to leave a certain amount of ink in the ink cartridge, taking into account the variation in the ejection amount.
Patent document 3 discloses a cartridge with an area therein for collecting air. Patent document 4 discloses an ink cartridge with two ink bags therein. However, if the ink cartridge is removed (from the apparatus) when both ink bags are empty and the negative pressure is high in the ink conveying path, air would enter the ink conveying path. Patent document 3 describes a method of removing air that has entered the cartridge. However, by employing such a method, the ink cartridge becomes complex and expensive.
Patent Document 1: Japanese Laid-Open Patent Application No. H8-645
Patent Document 2: Japanese Laid-Open Patent Application No. 2003-193340
Patent Document 3: Japanese Laid-Open Patent Application No. H11-182759
Patent Document 4: Japanese Laid-Open Patent Application No. H4-183116
In either of the above-described types of inkjet printers, it is desirable to completely consume the ink inside an ink cartridge. However, it is difficult to immediately detect an ink end status when the ink is completely consumed. If the ink end status is detected a few seconds after completely consuming the ink, the pressure in the middle of the ink conveying path may decrease, depending on the ink conveying method. Air may enter the ink supplying path and even the head tank by replacing the ink cartridge while the pressure is reduced. Air inside the ink supplying system may cause ink ejection failures in the inkjet recording apparatus.
If an attempt is made to convey ink from a completely empty ink cartridge or ink cartridge bag after the ink is completely consumed, the pressure inside the ink cartridge or ink cartridge bag decreases. When the ink cartridge or the ink cartridge bag is removed in such a status, the hollow needle for suctioning ink with reduced pressure therein contacts the atmospheric air. As a result, air from outside enters the ink feeding path through the needle hole.